A standard blister pack as for example used to hold pills comprises a relatively stiff base sheet formed of plastic with a uniform array of pocket-forming blisters each holding a respective one of the pills. A relatively weak cover foil, typically aluminum, is adhered to a front face of the base sheet so as to close the pockets. A pill is removed from the pack by pressing its pocket forward, thereby deforming it and forcing the pill through the cover foil. In this manner the pills are kept separate in respective hermetically closed compartments until used, and it is very easy to keep track of how many have been taken and how many are left.
Making such a pack child proof or resistant is fairly difficult, as not only are the pills an often attractive item, but pushing them out can be considered amusing to a young child. If the foil is made tough enough that small fingers do not have the strength to force a pill through them, the pack becomes difficult to use for the elderly or infirm.
Hence it has been suggested in U.S. Pat. No. 5,150,793 of Tannenbaum to provide a device that holds the pack. This device wraps around the pack and has a front wall that overlies the foil-covered front face of the pack and that is formed with an array of holes matching the array of pockets of the pack. The pack can move in the device between a position with its pockets aligned with the holes in the device and a position with the pockets offset from the holes in the device. In addition the pack is formed with a spring-like end region that bears against the end of the protective device and that urges the pack into the misaligned position in which the pills cannot be forced through the holes in the device. Thus the user must use so-called biaxial movement, that is must shift the pack to the side against the spring force and then, while holding it against the spring force in this position, push out the desired pill.
Such a system is relatively effective in preventing a child from getting at the pills and also in fact prevents inadvertent pushing-out of pills. It is however relatively complex and adds considerably to the packaging costs for the pills.